Catheters are flexible tubes used for navigating internal body vessels and lumens and guiding devices within the body, such as in the vasculature, urinary tract, spinal column, fallopian tubes, bile ducts, and the like, and are often used in connection with minimally invasive diagnostic or surgical techniques. Catheters may be used for medical procedures to examine, diagnose and treat internal conditions while positioned at a target location within the body that is otherwise inaccessible. An intravascular catheter, for example, is generally inserted and advanced through a valved introducer fitting into a blood vessel near the surface of the body, such as the femoral artery, and is guided through the vasculature to a desired location. Catheters are used for coronary vascular and cardiac-related interventional operations, as well as neurovascular interventions, peripheral vascular, renal, and other types of intravascular interventions. Medical devices and instruments may be guided, through the catheter, to the desired site and operated.
Catheters must generally be flexible enough to readily navigate a tortuous path, such as a path through tortuous vasculature, without getting stuck at tight turns, and without damaging tissue. Catheters must also be stiff enough to provide “pushability” along a path, such as through the vasculature. When catheters are used as a conduit for various tools, interventional devices, fluids, and the like, they provide support for internally guided tools, devices, fluids, etc., and they and must maintain a generally consistent internal configuration and avoid kinking during navigation to and from an interventional site and during operation at the interventional site. Infusion or withdrawal of liquids through the lumen of the tubular structure may be accomplished through a lumen provided by the catheter and, in this case, the structure of the catheter must have sufficient stiffness to resist both collapse and expansion of the lumen under a range of pressures and force conditions. Thus, it is essential that catheter structures used in connection with such devices be as flexible as possible during placement and removal yet have a high degree of structural integrity, permitting the catheter to be navigated and to serve as a conduit for fluids and internal structures during and/or following placement.
Many catheters have a composite construction that provides greater stiffness and support in certain areas, such as proximal areas, and more flexibility in other areas, such as distal areas. Variable stiffness along the length of a catheter is typically provided by varying the construction and/or diameter and/or wall thickness and/or material composition along the length of the catheter. There are many examples of catheters having variable stiffness along their lengths in the prior art literature. Some previous attempts at designing a kink-resistive tubular structure provided a layer of a coiled, braided or otherwise weaved member that has tight loops and that is fixedly attached to or embedded in a polymeric layer, such as a polyimide or plastic layer. Although the construction of the layer may allow for a small amount of flexibility, the use of a woven or coiled layer attached to or embedded in a polymeric layer generally results in a tubular structure that is stiffer in portions of the structure than which is required by many applications. Some tubular structure designs that include such layers are described in U.S. Pat. Nos. 6,464,684; 6,197,014; and 5,868,767. U.S. Patent Publication US-2004-0230212-A1 discloses a different type of catheter structure providing a lumen, an overlying layer and a coil element support layer that is attached to the overlying layer at a bonding point but otherwise slippable relative to the overlying layer. This slippable relationship between the coil element and an overlying layer improves flexibility and reduces kinking
Many types of catheters include reinforcing structures, such as tubular structures, along at least an area of their length. Tubular members used in catheter construction may have a reduced diameter and/or a reduced wall thickness along at least an area of their length to provide increased flexibility, and may additionally be scored or cut to increase their flexibility. U.S. Pat. No. 4,960,410 discloses, for example, a relatively stiff tube that is spirally scored or cut along a portion of its length, such as the distal portion, to increase its flexibility. The spirally cut or scored tube is covered by a more flexible tube. U.S. Pat. No. 5,573,520 discloses a catheter structure in which a self-supporting tube having a plurality of apertures, such as spiral apertures or discontinuous slots, is encased by a covering to provide a catheter structure providing a lumen having a fluid-tight seal. U.S. Pat. No. 5,599,326 disclose a catheter section including an elongate tubular member comprising an inner stiffener liner of a spirally cut polymeric tubing member and an outer tubular cover comprising a polymeric cover material. U.S. Pat. No. 5,843,050 discloses diagnostic and/or therapeutic microcatheters that are highly flexible and may have a tubular wall with two coaxial tubular elements in the wall, each of the tubular elements provided with a spiral cut in its distal zone to increase flexibility.
U.S. Pat. No. 6,048,338 describes various types of catheters having an elongate shaft with a transition in flexibility and a transition tube disposed about the shaft and having a spiral cut, easing bending of the shaft. The transition tube may have only one end secured to the catheter shaft, and the pitch of the spiral cut may be varied. U.S. Pat. No. 6,254,588 discloses a catheter having a spiral cut tubular member within a flexible body having at least one flexibility gradient zone, with a different flexibility at a proximal end and at a distal end, and having a continuous change in flexibility between the two. Yet another patent, U.S. Pat. No. 6,652,508, proposes an intravascular catheter comprising a distal flexible tube having a spiral slot with coils disposed in the voids formed by the slots.
U.S. Patent Publication 2006/0100687 discloses a delivery catheter assembly having an inner metallic hypotube and an outer metallic hypotube, each of the hypotubes having spiral or circumferential slots interrupted at intervals by solid struts. The distal end of the tubes may have smaller pitch slots, and the proximal end of the tubes may have larger pitch slots to vary the flexibility along the length of the catheter. U.S. Patent Publication 2009/0062602 discloses a flexible spine for use in a catheter or a sheath. The flexible spine is composed of a unitary structure having a plurality of discrete sections, each of which has a distinguishing structural attribute that differentiates it from other sections, wherein the arrangement of sections varies flexibility. An aperture structure having an expanded or enlarged I-shape, or a double-ended vase shape is disclosed.
Notwithstanding the numerous disclosures relating to catheter structures and the numerous types of catheters and sheaths available, improvements in catheter flexibility, versatility, pushability and other properties are highly desirable. The present invention is thus directed to sheath assemblies having improved properties for use with interventional catheter systems and interventional catheter systems incorporating such sheath assemblies.